Field of the Invention
The present invention relates to an ink, an ink cartridge, and an image recording method.
Description of the Related Art
An ink jet recording method is one of the image recording methods that have been significantly developing in recent years because a high-quality color image can be easily recorded by the method despite the fact that its principle is simple. In addition, the method has rapidly become widespread not only in the image recording of a document, a photograph, and the like in households that has heretofore been a mainstream but also in offices and industrial applications.
In the case of a printer for a household or for an office, printing is performed by scanning the recording surface of a recording medium with a short serial type head a plurality of times, and hence a printing speed is limited. Meanwhile, a long line type head has been developed in recent years. When a recording apparatus, such as a printer, mounted with such line type head is used, an image of a size corresponding to a head width can be recorded by one scan (one pass). Accordingly, the ink jet recording method has started to be adopted also in a commercial printing industry where printing at higher speed is required.
In the commercial printing industry, it is necessary that a large amount of images can be printed at lower cost. Accordingly, it has been desired that a high-quality image can be recorded not only on inexpensive and thin paper that has been generally called printing paper and has been widely used but also on thin paper free of an ink-receiving layer that has been called plain paper.
In the recording of an image on the plain paper, fixability showing a time period from the time point when an ink applied to the recording medium is brought into contact with a member in a recording apparatus, such as a conveying roller, to the time point when the ink stops contaminating the member, and the optical density of the image have heretofore been important setting items. Meanwhile, inks that have been sold in the market are roughly classified into a so-called superpermeable ink (ink having high permeability into the recording medium) placing emphasis on the fixability, and a so-called overlay ink (ink having low permeability into the recording medium) placing emphasis on the optical density of the image.
The superpermeable ink contains a large amount of a permeable solvent (e.g., a glycol ether or a diol), and an ink droplet applied to the surface of the recording medium (plain paper) permeates a gap between cellulose fibers constituting the plain paper. The ink has a feature of having a quick permeation time of the order of milliseconds.
In the overlay ink, an ink droplet applied to the surface of the recording medium permeates a cellulose fiber itself, and hence its permeation time into the recording medium is at a level of several seconds. Accordingly, a coloring material remains in a portion relatively close to the surface of the recording medium, and hence the optical density can be efficiently increased. In Japanese Patent Application Laid-Open No. H05-179183, there is a disclosure of an overlay ink whose pigment fixes to the vicinity of the surface of plain paper.